the earth’s - montana state university billings 2010/suits/geo... · • of what is the earth’s...
TRANSCRIPT
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The Earth’s Atmosphere,
Climate and Weather
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• Of what is the Earth’s atmosphere made?
• Where did the earth’s atmosphere come from?
• Has the Earth’s atmosphere always been the same?
• Is there evidence that life forms have affected the atmosphere?
• What is the Ozone layer and what does it do?
• Can we expect the atmosphere to change in our lifetimes?
• What causes atmospheric pressure?
• How does atmospheric pressure change with altitude
• What are the different layers of the atmosphere and on what basis are they defined?
• How is heat get from one place to another?
• What is the Greenhouse Effect and what causes the seasons?
Questions
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Spheres Timescales
extraterrestrial
Cosmos billions of years
terrestrial
Lithosphere millions of years
Pedosphere 100s to 1000s of years
Hydrosphere days to 1000s of years
Atmosphere minutes to 1000s of years
Biosphere seconds to 1000s of years
Noösphere seconds to 10s of years
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Atmospheric Composition
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Present Atmosphere
Nitrogen (N2) 78%
Oxygen (O2) 21%
Argon (Ar) 1%
Carbon Dioxide (CO2) 0.039% >> 390 ppm
Water (H2O) 0 to 4%
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Present Atmosphere
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The Hole in the Ozone Layer!It appears in the winter
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Where did the present atmosphere come from?
Or,
Why is there air?
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Formation of the Earth’s Atmosphere
First Atmosphere was like the Solar Nebula• Mostly Hydrogen and Helium• Would have been quickly lost because the Earth’s gravity is not great enough to either hold H or He at this temperature
A second atmosphere was produced by gases from volcanoes and comets from outer space. CO2 concentrations were probably very high.
Photosynthesis in particular changed this atmosphere by adding oxygen
Other changes continue today
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Earth’s first atmosphere (H and He) was similar to that of Saturn’s
moon: Titan
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In the early Earth, gases would emanate from volcanic
eruptions like this one on the big island of Hawaii
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Secondary Atmosphere - Outgassing
Initially Composed of:• Ammonia (NH3)• Hydrogen (H2)• Carbon dioxide (CO2)• Methane (CH4)• Water vapor (H2O)• Nitrogen (N2)•But NO OXYGEN!
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No Oxygen!
Evidence:• No Rust Minerals
• Conglomerates made of Pyrite and Uraninite(these would rapidly oxidize and dissolve today)
Witwatersrand conglomerate, South Africa
(Middle Archean)
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photosynthesis
CO2 + H2O CH2O + O2Carbon dioxide Water Carbohydrate Oxygen
Where atmospheric Oxygen comes from
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Photosynthesis and Respiration
CO2 + H2O CH2O + O2
Photosynthesis Requires energy input
aerobic Respiration Gives off energy
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NASA/Goddard Space Flight Center, The SeaWiFS Project and GeoEye, Scientific Visualization Studio
SeaWiFS Biosphere: 3 years
GlobalProd_Seawifs.mpg
First a look at photosynthesis in the modern world and then back to the early Earth…..
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Atmospheric EvolutionPrimary - Captured from Solar Nebula
- Mostly Hydrogen and Helium- Quickly Lost
Secondary - Formed by Outgassing by Volcanoes
Tertiary - Modified by Life (addition of Oxygen)
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The Oceans rain down as the Earth cools
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However, every once in a while…
Oceans were vaporized by large impacts
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But eventually things settled down a few billion
years ago and we ended up with modern Oceans
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IG4e_02_01
Quick radiation review
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Electromagnetic Radiation
- Everything above -273˚C (absolute zero, 0 Kelvin) emits radiation
- Hotter objects emit more energy at shorter wavelengths
- Colder objects emit more energy at longer wavelengths
Figure 2.2, p. 53
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Shortwave and Longwave Radiation
The hot sun radiates at shorter wavelengths that carry more energy,
Energy absorbed by the cooler earth is then re-radiated at longer wavelengths, as predicted by Wein's law.
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Electromagnetic Radiation
Figure 2.2, p. 53
Sun
Earth
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Two Faces of Solar Energy
Ultra violet Visible
10 meters
Lethal Energy source for life forms
Ultraviolet rays absorb ozone (O3)in the stratosphere
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Ozone is good in the stratosphere but bad in the troposphere
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Atmospheric Pressure• Molecules bumping into an object create a
force on that object
• Pressure is the force applied per unit area
P = Force/Area; where gravity is the force in atmospheric pressure
Which box below is exerting the greatest pressureupon the ground?
1 kg 1 kg
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Pressure and Density of the Atmosphere
• Gravity holds most of the air close to the ground
• The weight of the overlying air is the pressure at any point
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Vertical Structure
The world is a big place, but the atmosphere is very shallow. Consider …
• In Billings, about 12% of the mass of the atmosphere is below our feet
• At the top of Beartooth (~11000 ft), you are above ~30% of the atmosphere’s mass
• You are closer to outer space than to Bozeman!
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Temperature Scales
• In the US, we use Fahrenheit
• Celsius (centigrade) is a scale based on freezing/boiling of water
• Kelvin is like centigrade, but starts at absolute zero (-275°C)
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Atmospheric Soundings
Helium-filled weather balloons are released from over 1000 locations around the world every 12 hours (some places more often)
These document temperature, pressure, humidity, and winds aloft
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The atmosphereis layered accordingto its temperaturestructure
In some layersthe temperatureincreases with height
In others it decreaseswith height or is constant
Why?
… “pause” is a level
… “sphere” is a layer
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Vertical Thermal Structure
• Heated in thermosphere by O2
and N2 absorption
• Heated in stratosphere by ozone absorption
• Heated from below by latent and sensible heat fluxes
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Lower in the Atmosphere
We live here
What layer is that ?
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Transfer of Heat
• Conduction - Where molecules transfer energy by coming into contact with one another.
• Convection - Where a fluid moves from one place to another, carrying it’s heat energy with it.– In atmospheric science, convection is usually associated
with vertical movement of the fluid (air or water).
– Advection is the horizontal component of the classical meaning of convection.
• Radiation - The transfer of heat by radiation does not require contact between the bodies exchanging heat, nor does it require a fluid between them.
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Conduction – Direct Heat Transfer
Conduction of heat energy occurs as warmer molecules transmit vibration, and hence heat, to adjacent cooler molecules.
Warm ground surfaces heat overlying air by conduction.
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Radiation– heat transferred even in a vacuum!
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Heat driven convection
1. Bottom water is warmed
2. It expands an is therefore less dense
3. It rises to the surface
4. and then spreads out to the sides
5. Cooler water at the sides sinks
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Inside of stars
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Inside of the Earth
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In the lower troposphere during about every summer day
Convective thunderstorms caused by surface heating, rising buoyant plumes, and the release of
latent heat in clouds
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A convective thunderstorm
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‘convective’ tornadoes
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Hurricanes
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Convection in a hurricane
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Mid Latitude Cyclones
Rising air in the center of a low pressure zone is the driving force in most storms
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Temperature, Density, and Convection
Heating of the Earth’s surface during daytime causes the air to mix
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Warmed from Below
Solar radiation passes first through the upper atmosphere, but only after absorption by earth's surface does it generate sensible heat to warm the ground and generate longwaveenergy.
This heat and energy at the surface then warms the atmosphere from below.
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Molecular Structure of Water
Water's unique molecular structure and hydrogen bonds enable all 3 phases to exist in earth's atmosphere.
water moleculeice
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Molecular Structure of Water
Water's unique molecular structure and hydrogen bonds enable all 3 phases to exist in earth's atmosphere.
ice
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Energy associated with phase change
80 calories 100 calories 540 calories!
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The Earth’s Radiation Balance
Incoming Energy = Outgoing Energy
(absorbed sunshine)(area) = (thermal loss)(area)
S(1-a)pr2 = s T4 (4 pr2)
Solve for TT = -18° C; (0°F)
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The radiative equilibrium temperature
The equilibrium surface temperature should be -18°C (~0°F) .
But, the observed surface temperature is
+15°C (~60°F).
Why?
We have an atmosphere
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Solar Radiation
30% reflected
~50% absorbed by the surface
20% absorbed by the
atmosphere
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Greenhouse Effect
Heat radiated by the Earth’s surface is absorbed by gases in the atmosphere and
reradiated back to the Earth
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Carbon Dioxide (CO2) ConcentrationsCombustion of fossil fuels (coal and oil) by humans has increased concentrations of some greenhouse gases
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Scattering: Why is the sky blue?
• Sunlight is scattered by air molecules
• Shorter wavelengths (green, blue, violet) scattered more efficiently
• Unless we are looking directly at the sun, we are viewing light scattered by the atmosphere
• Finally, blue dominates over violet because our eyes are more sensitive to blue light
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Why are Sunsets Red?• The sun appears fairly white
when it’s high in the sky
• Near the horizon, sunlight must penetrate more atmosphere and therefore, there is more scattering of blue and other shorter wavelengths
• The orange sunset occurs because longer wavelengths, such as orange and yellow, make it through
• If there are a lot of particulates, yellow will be scattered as well
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Seasons & Sun's Distance
Earth is 5 million kilometers further from the sun in July than in January, indicating that seasonal warmth is controlled by more than solar proximity.
Figure 3.1
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Solstice & Equinox
• Earth's tilt of 23.5° and revolution around the sun creates seasonal solar exposure and heating patterns
• At solstice, tilt keeps a polar region with either 24 hours of light or darkness
• At equinox, tilt provides exactly 12 hours of night and 12 hours of day everywhere
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Solar intensity, defined as the energy per area, governs Earth's seasonal climate changes
A sunlight beam that strikes at an angle is spread across a greater surface area, and is a less intense heat source than a beam impinging directly.
Seasons & Solar Intensity
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Hours of daylight and Latitude
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Midnight Sun
The region north of the Arctic Circle experiences a period of 24 hour sunlight in summer, where the Earth's surface does not rotate out of solar exposure
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Take home message
• Seasons are regulated by the amount of solar energy received at Earth’s surface, which depends upon:
– angle at which sunlight strikes Earth’s surface.
– how many hours the sun shines per day.
• Seasons are NOT due to the elliptical nature of the earth’s orbit, i.e. changes in distance from the Sun.